1. Field of the Invention
The present invention relates to soft magnetic films which contain a CoFexcex1 alloy (the element xcex1 is Ni or the like) used as, for example, core materials of thin-film magnetic heads and which have superior corrosion resistance and a higher saturated magnetic flux density Bs than an NiFe alloy. In addition, the present invention relates to thin-film magnetic heads using the soft magnetic films described above, to methods for manufacturing the soft magnetic films, and to methods for manufacturing the thin-film magnetic heads.
2. Description of the Related Art
In particular, concomitant with the recent trend toward higher recording densities, it has become necessary that, in order to improve a recording density, a magnetic material having a higher saturated magnetic flux density Bs be used for forming a core layer of a thin-film magnetic head so that a magnetic flux is concentrated in the vicinity of the gap of the core layer.
An NiFe alloy has been frequently used for the magnetic material described above. The NiFe alloy described above is formed by an electroplating method using a DC current and is able to have a saturated magnetic flux density Bs of approximately 1.8 T.
In order to further increase the saturated magnetic flux density Bs of the NiFe alloy, for example, an electroplating method using a pulse current is used in place of an electroplating method using a DC current.
According to the method described above, the Bs of the NiFe alloy can be increased; however, the saturated magnetic flux density Bs cannot be increased to 2.0 T or more. In addition, the surface roughness of the film is increased, and hence, there has been a problem in that the NiFe alloy is corroded by various solvents used in a process for forming a thin-film magnetic head.
From the NiFe alloy described above, a soft magnetic film having a high saturated magnetic flux density Bs together with superior corrosion resistance has not been formed.
In addition to the NiFe alloy, as a soft magnetic material which is frequently used, a CoFe alloy film may be mentioned. When the component ratio of Fe is appropriately controlled, the CoFe alloy film may have a higher saturated magnetic flux density Bs than that of an NiFe alloy film; however, it has the following problem.
Depending on the structure of a thin-film magnetic head or another magnetic element, an NiFe alloy may be overlaid on the CoFe alloy in some cases. In the case described above, when the NiFe alloy film is formed on the CoFe alloy film by an electroplating method, the CoFe alloy film may be ionized and dissolved out, and as a result, corrosion occurs.
The reason for this is that a significant potential difference (difference in standard electrode potential) is generated between the CoFe alloy film and the NiFe alloy film, and it is believed that a so-called battery effect is obtained by this potential difference and that the CoFe alloy film is dissolved out.
In addition to the NiFe alloy film and the CoFe alloy film described above, a CoFeNi film is also one of the soft magnetic films which are frequently used. For example, in Table 2 shown in U.S. Pat. No. 6,063,512, four CoFeNi alloy films having different compositions and soft magnetic properties thereof are listed.
However, according to the compositions of the CoFeNi alloy films described in this publication, the saturated magnetic flux densities Bs-thereof are all less than 2.0 T, and compared to a NiFe alloy film, a large saturated magnetic flux density Bs cannot be effectively obtained.
Accordingly, the present invention was made to solve the conventional problems described above, and an object of the present invention is to provide a soft magnetic film having a higher saturated magnetic flux density Bs than that of an NiFe alloy and superior corrosion resistance, the soft magnetic film containing a CoFexcex1 alloy having appropriate component ratios; a thin-film magnetic head using the soft magnetic film described above; a method for manufacturing the soft magnetic film; and a method for manufacturing the thin-film magnetic head.
In addition, the present invention also provides a soft magnetic film which comprises a CoFexcex1 alloy and which can maintain a high saturated magnetic flux density Bs, in which the CoFexcex1 alloy is prevented from being dissolved out when an NiFe alloy is formed thereon by plating; a thin-film magnetic head using the soft magnetic film described above; a method for manufacturing the soft magnetic film; and a method for manufacturing the thin-film magnetic head.
In accordance with one aspect of the present invention, a soft magnetic film has a composition represented by the formula CoxFeyxcex1z (the element xcex1 is at least one of Ni and Cr), wherein the component ratio X of Co is 8 to 48 mass %, the component ratio Y of Fe is 50 to 90 mass %, the component ratio Z of the element xcex1 is 2 to 20 mass %, and the equation X+Y+Z=100 mass % is satisfied.
When a CoFexcex1 alloy has the composition described above, the saturated magnetic flux density Bs thereof can be 2.0 T or more. As described above, in the present invention, a higher saturated magnetic flux density Bs than that of an NiFe alloy can be obtained.
In addition, the formation of coarse crystal grains can be suppressed, dense crystals can be formed, and hence, the surface roughness can be decreased. Accordingly, in the present invention, a soft magnetic film having a high saturated magnetic flux density Bs of 2.0 T or more and, in addition, superior corrosion resistance can be manufactured.
In the present invention, it is preferable that the component ratio X of Co be 23 to 32 mass %, the component ratio Y of Fe be 58 to 71 mass %, the component ratio Z of the element xcex1 be 2 to 20 mass %, and the equation X+Y+Z=100 mass % be satisfied.
When a CoFexcex1 alloy has the component ratios in the ranges described above, the saturated magnetic flux density Bs thereof can be 2.15 T or more. In addition, the center line average roughness Ra of the film surface can be 5 nm or less, and the corrosion resistance can be more effectively improved.
In addition, in the present invention, it is more preferable that the component ratio X of Co be 23.3 to 28.3 mass %, the component ratio Y of Fe be 63 to 67.5 mass %, the component ratio Z of the element xcex1 be 4.2 to 13.6 mass %, and the equation X+Y+Z=100 mass % be satisfied. Consequently, the saturated magnetic flux density Bs can be 2.2 T or more. In addition, the center line average roughness Ra of the film surface can be 5 nm or less, and the corrosion resistance can be more effectively improved.
Furthermore, in the present invention, it is most preferable that the component ratios, X of Co, Y of Fe, and Z of the element xcex1, be in the area surrounded by three points (X, Y, and Z) of (26.5, 64.6, and 8.9 mass %), (25.5, 63, and 11.5 mass %), and (23.3, 67.5, and 9.2 mass %), and the component ratios satisfy the equation X+Y+Z=100 mass %. Consequently, the saturated magnetic flux density Bs can be more than 2.2 T. In particular, it was confirmed by the experiments described below that the saturated magnetic flux density Bs could be increased up to 2.25 T. In addition, the center line average roughness Ra of the film surface can be 5 nm or less, and the corrosion resistance can be more effectively improved.
In the present invention, a passivation film is preferably formed on a surface of the soft magnetic film. The passivation film is a dense oxide film and is formed by the presence of Ni or Cr in the soft magnetic film.
In the case in which the passivation film is formed on the surface of the soft magnetic film as described above, the CoFexcex1 alloy can be prevented from being ionized and dissolved out even when an NiFe alloy film is formed on the soft magnetic film by plating.
Accordingly, in the present invention, even when an NiFe alloy film is formed on the CoFexcex1 alloy film by plating, a high saturated magnetic flux density Bs and superior corrosion resistance of the CoFexcex1 alloy can be appropriately maintained.
In the present invention, the soft magnetic film is preferably formed by plating. Consequently, a soft magnetic film having an optional thickness can be formed, and a film thickness larger than that formed by sputtering can be obtained.
A thin-film magnetic head in accordance with another aspect of the present invention comprises a lower core layer composed of a magnetic material, an upper core layer formed above the lower core layer with a magnetic gap provided therebetween, and a coil layer for supplying a recording magnetic field to the lower core layer and the upper core layer described above, wherein at least one of the lower core layer and the upper core layer is formed of the soft magnetic film described above.
In addition, the thin-film magnetic head described above may further comprise a bulged lower magnetic pole layer formed on the lower core layer so as to be exposed to an opposing surface opposing a recording medium, and the lower magnetic pole layer is preferably formed of the soft magnetic film described above.
A thin-film magnetic head in accordance with another aspect of the present invention comprises a lower core layer, an upper core layer, and a magnetic pole portion provided between the lower core layer and the upper core layer, the width in the track width direction of the magnetic pole portion being formed smaller than that of each of the lower core layer and the upper core layer, wherein the magnetic pole portion comprises a lower magnetic pole layer in contact with the lower core layer, an upper magnetic pole layer in contact with the upper core layer, and a gap layer provided between the lower magnetic pole layer and the upper magnetic pole layer, or the magnetic pole portion comprises an upper magnetic pole layer in contact with the upper core layer and a gap layer provided between the upper magnetic pole layer and the lower core layer, and at least one of the upper magnetic pole layer and the lower magnetic pole layer is formed of the soft magnetic film described above.
In the thin-film magnetic head described above, it is preferable that the upper magnetic pole layer described above be formed of the soft magnetic film and that the upper core layer provided on the upper magnetic pole layer be an NiFe alloy film formed by plating.
In addition, in the present invention, it is preferable that at least one of the upper core layer and the lower core layer have a portion which is in contact with the magnetic gap and which is composed of at least two magnetic layers, or that at least one of the upper magnetic pole layer and the lower magnetic pole layer be composed of at least two magnetic layers, in which a magnetic layer in contact with the magnetic gap among the magnetic layers is formed of the soft magnetic film.
In the case described above, the magnetic layers other than the magnetic layer in contact with the magnetic gap layer are preferably composed of an NiFe alloy formed by plating.
As described above, the CoFexcex1 alloy of the present invention used as a soft magnetic film has a high saturated magnetic flux density Bs of 2.0 T or more, and the surface roughness is small. When this type of soft magnetic film is used for a core material of a thin-film magnetic head, the magnetic flux can be concentrated in the vicinity of the gap, the trend toward higher recording densities can be facilitated, and hence, a thin-film magnetic head having superior corrosion resistance can be manufactured.
In accordance with another aspect of the present invention, a method for manufacturing a soft magnetic film comprises a step of forming a CoxFeyxcex1z alloy film by electroplating in a plating solution using a pulse current, wherein the component ratio X of Co is 8 to 48 mass %, the component ratio Y of Fe is 50 to 90 mass %, the component ratio Z of the element xcex1 (the element xcex1 is at least one of Ni and Cr) is 2 to 20 mass %, and the equation X+Y+Z=100 mass % is satisfied.
The Fe content has a significant influence on the saturated magnetic flux density Bs. When the Fe content is small, the Bs is decreased. According to a CoFeNi alloy shown in Table 2 in U.S. Pat. No. 6,063,512, the Fe content is up to 30 mass %, and it is believed that a low Fe content as described above may be one reason responsible for decreasing the saturated magnetic flux density BS to less than 2.0 T.
In addition, by a conventional electroplating method using a DC current, it has been difficult to increase the Fe content. In order to increase the Fe content in a film, for example, the Fe ion concentration in a plating solution was increased; however, there had been a limitation, and a CoFeNi alloy having a saturated magnetic flux density Bs of 2.0 T or more could not be obtained.
Accordingly, in the present invention, the CoFexcex1 alloy is formed by electroplating using a pulse current. In the electroplating using a pulse current, for example, on and off operations of a current controlling element are repeatedly performed so that there are periods in which a current flows and periods in which current does not flow during plating. Since there are periods in which current does not flow, a CoFexcex1 alloy film is gradually formed by plating, and the deviation of current density distribution during plating can be reduced compared to that of a conventional electroplating method using a DC current. According to the electroplating using a pulse current, the Fe content in the soft magnetic film can be easily controlled compared to that of the electroplating using a DC current, and hence, the Fe content in the film can be increased.
According to the present invention, the component ratio Y of Fe can be 50 to 90 mass %. According to the component ratio mentioned above, it was found by the experiments described later that the saturated magnetic flux density Bs could be 2.0 T or more. Concerning the component ratios of Co and the element xcex1, when the element xcex1 is excessively contained, it was found by the experiments described later that the saturated magnetic flux density Bs was decreased to less than 2.0 T. According to the present invention, when the component ratio X of Co is set to 8 to 48 mass %, and the component ratio Z of the element xcex1 is set to 2 to 20 mass %, a CoFexcex1 alloy having a saturated magnetic flux density Bs of 2.0 T or more and superior corrosion resistance can be manufactured.
According to the present invention, the plating is preferably performed in a plating solution having a ratio of Fe ion concentration to Co ion concentration of 1.5 or more and a ratio of Fe ion concentration to a ion concentration of 2 to 4, whereby a CoxFeyxcex1z alloy film is formed in which the component ratio X of Co is 23 to 32 mass %, the component ratio Y of Fe is 58 to 71 mass %, the component ratio Z of the element xcex1 is 2 to 20 mass %, and the equation X+Y+Z=100 mass % is satisfied.
As shown in the experiments described later, in the CoFexcex1 alloy formed in the plating solution having the ratios of ion concentration described above, the saturated magnetic flux density Bs can be 2.15 T or more, the center line average roughness of the film surface can be 5 nm or less, and hence, a soft magnetic film having a high saturated magnetic flux density Bs and superior corrosion resistance can be manufactured by plating.
According to the present invention, the plating is more preferably performed in a plating solution having a ratio of Fe ion concentration to Co ion concentration of 1.5 or more and a ratio of Fe ion concentration to xcex1 ion concentration. of 2 to 3.4, whereby a CoxFeyxcex1z alloy film is formed in which the component ratio X of Co is 23.3 to 28.3 mass %, the component ratio Y of Fe is 63 to 67.5 mass %, the component ratio Z of the element xcex1 is 4.2 to 13.6 mass %, and the equation X+Y+Z=100 mass % is satisfied. As shown in the experiments described later, in the CoFexcex1 alloy formed in the plating solution having the ratios of ion concentration described above, the saturated magnetic flux density Bs can be 2.2 T or more.
According to the present invention, the plating is most preferably performed in a plating solution having a ratio of Fe ion concentration to Co ion concentration of 1.7 or more and a ratio of Fe ion concentration to a ion concentration of 2 to 3.4, whereby a CoxFeyxcex1z alloy film is formed in which the component ratios, X of Co, Y of Fe, and Z of the element xcex1, are in the area surrounded by three points (X, Y, and Z) of (26.5, 64.6, and 8.9 mass %), (25.5, 63, and 11.5 mass %), and (23.3, 67.5, and 9.2 mass %), and the equation X+Y+Z=100 mass % is satisfied. As shown in the experiments described later, in the CoFexcex1 alloy formed in the plating solution having the ratios of ion concentration described above, the saturated magnetic flux density Bs can be more than 2.2 T.
In the present invention, the plating solution preferably contains sodium saccharin. Sodium saccharin (C6H4CONNaSO2) serves as a stress relaxation agent; hence, when the sodium saccharin is contained, the film stress of the CoFexcex1 alloy can be reduced.
In the present invention, the plating solution preferably contains 2-butyne-1,4-diol. Accordingly, the formation of coarse crystal grains of the CoFexcex1 alloy formed by plating is suppressed, the particle diameter of the crystal grains is decreased, and it is unlikely that voids would be generated between the crystals, whereby the surface roughness of the film is decreased. Since the surface roughness can be decreased, the coercive force Hc can also be decreased.
In the present invention, the plating solution preferably contains sodium 2-ethylhexyl sulfate. Accordingly, since hydrogen generated in the plating solution is removed by the sodium 2-ethylhexyl sulfate which serves as a surfactant, the surface roughness caused by the adsorption of the hydrogen to the plating film can be suppressed.
In addition, in place of the sodium 2-ethylhexyl sulfate, sodium lauryl sulfate may be used. However, when sodium 2-ethylhexyl sulfate is contained in a plating solution, the generation of bubbles is not significant compared to the case of using sodium lauryl sulfate, and a larger amount of sodium 2-ethylhexyl sulfate can be contained in the plating solution, whereby the hydrogen can be appropriately removed.
In accordance with another aspect of the present invention, a method for manufacturing a thin-film magnetic head, which includes a lower core layer composed of a magnetic material, an upper core layer opposing the lower core layer at an opposing surface opposing a recording medium with a magnetic gap provided therebetween, and a coil layer supplying a recording magnetic field to the two core layers described above, comprises a step of forming at least one of the lower core layer and the upper core layer composed of a soft magnetic film by plating in accordance with the manufacturing method described above.
The method described above may further comprise a step of forming a bulged lower magnetic pole layer on the lower core layer so as to be exposed to the opposing surface opposing the recording media, wherein the bulged lower magnetic pole layer is preferably formed of the soft magnetic film by plating.
In accordance with another aspect of the present invention, a method for manufacturing a thin-film magnetic head, which includes a lower core layer, an upper core layer, and a magnetic pole portion which is provided between the lower core layer and the upper core layer and which has the width in the track width direction formed smaller than that of each of the lower core layer and the upper core layer, comprises a step of forming a lower magnetic pole layer in contact with the lower core layer, an upper magnetic pole layer in contact with the upper core layer, and a gap layer provided between the lower magnetic pole layer and the upper magnetic pole layer so as to form the magnetic pole portion; or a step of forming an upper magnetic pole layer in contact with the upper core layer and a gap layer provided between the upper magnetic pole layer and the lower core layer so as to form the magnetic pole portion, wherein at least one of the upper magnetic pole layer and the lower magnetic pole layer is formed of the soft magnetic film by plating according to the manufacturing method described above.
In the method described above, it is preferable that the upper magnetic pole layer be formed of the soft magnetic film by plating and that the upper core layer be formed of an NiFe alloy film by electroplating on the upper magnetic pole layer.
In the method described above, it is preferable that at least one of the upper core layer and the lower core layer have a portion which is in contact with the magnetic gap and which is composed of at least two magnetic layers, or that at least one of the upper magnetic pole layer and the lower magnetic pole layer be composed of at least two magnetic layers, in which a magnetic layer in contact with the magnetic gap among the magnetic layers is formed of the soft magnetic film described above.
In the present invention, the magnetic layers other than the magnetic layer in contact with the magnetic gap layer are preferably formed of an NiFe alloy by electroplating.
As described above, when the CoFexcex1 alloy used as the soft magnetic film of the present invention is formed by electroplating using a pulse current, a CoxFeyxcex1z alloy can be formed in which the component ratio X of Co is of 8 to 48 mass %, the component ratio Y of Fe is 50 to 90 mass %, the component ratio Z of the element xcex1 is 2 to 20 mass % (the element xcex1 is at least one of Ni and Cr), and the equation X+Y+Z=100 mass % is satisfied.
In addition, when the soft magnetic film described above is used as a core material of a thin-film magnetic head, the saturated magnetic flux density Bs can be increased, and hence, a higher recording density can be achieved. In addition, a thin-film magnetic head having superior corrosion resistance can be manufactured in a high yield.